题目：给一个不多于5位的正整数，要求：一、求它是几位数，二、逆序打印出各位数字。  

程序设计：

import java.util.Scanner;
public class Ex24 {
public static void main(String[] args) {
   Ex24 tn = new Ex24();
   Scanner s = new Scanner(System.in);
   long a = s.nextLong();
   if(a < 0 || a > 100000) {
    System.out.println("Error Input, please run this program Again");
    System.exit(0);
   }
    if(a >=0 && a <=9) {
    System.out.println( a + "是一位数");
    System.out.println("按逆序输出是" + '\n' + a);
   } else if(a >= 10 && a <= 99) {
    System.out.println(a + "是二位数");
    System.out.println("按逆序输出是" );
    tn.converse(a);
   } else if(a >= 100 && a <= 999) {
    System.out.println(a + "是三位数");
    System.out.println("按逆序输出是" );
    tn.converse(a);
   } else if(a >= 1000 && a <= 9999) {
    System.out.println(a + "是四位数");
    System.out.println("按逆序输出是" );
    tn.converse(a);
   } else if(a >= 10000 && a <= 99999) {
    System.out.println(a + "是五位数");
    System.out.println("按逆序输出是" );
    tn.converse(a);
   }
}
public void converse(long l) {
   String s = Long.toString(l);
   char[] ch = s.toCharArray();
   for(int i=ch.length-1; i>=0; i--) {
    System.out.print(ch[i]);
   }
}
}